Graphics and video display systems, such as displays for computer systems, terminals and televisions, are typically comprised of an array of addressable picture elements (pixels). Source pixel data is first formatted by an associated control circuit, and then loaded into the pixel array one frame at a time. This pixel data may be written to the pixel array using a variety of algorithms, i.e. sequentially top-to-bottom one pixel line at a time, interleaving by sequentially addressing top-to-bottom every other pixel line, such as the odd rows of pixels, and then returning to address the even pixel lines, etc. In cathode ray tubes (CRTs) this data writing technique is known as rasterizing, whereby a high powered electrode gun scans across the pixel elements of a phosphor screen left to right, one line at a time. This data writing scheme is applicable to liquid crystal displays (LCD's) as well.
Irregardless of the algorithm implemented to load the pixel array with a frame of pixel data, the pixel array needs to display at least 20 frames of data per second for the human eye to perceive a smooth motion picture. If the pixel array displays less than 20 frames of video data per second, the displayed image will appear as a series of stepped discrete picture frames.
A recent innovation of Texas Instruments Incorporated of Dallas Tex., is the digital micro-mirror device (DMD). The DMD is suitable for use in displays, projectors and hard copy printers. The DMD is a monolithic single-chip integrated circuit spatial light modulator (SLM), comprised of a high density array of 17 micron square movable micro mirrors. These mirrors are fabricated over an address circuitry including an array of SRAM cells and address electrodes. Each mirror forms one pixel of the DMD array and is bi-stable, that is to say, stable in one of two positions, wherein a source of light directed upon the mirror array will be reflected in one of two directions. In one stable "on" mirror position, light will be reflected to a collector lens and focused on a display screen. In the other "off" mirror position, light directed on the mirror will be deflected to a light absorber. Each mirror of the array is individually controlled to either direct light into the collector lens, or to the light absorber. The collector lens and a light prism ultimately focus and magnify light from the pixel mirrors onto a display screen and produce an image. If each pixel mirror of the DMD array is in the "on" position, the image will be an array of bright pixels.
For a more detailed discussion of the DMD device, cross reference is made to U.S. Pat. No. 5,061,049 to Hornbeck, entitled "Spatial Light Modulator and Method"; U.S. Pat. No. 5,079,544 to DeMond, et al, entitled "Standard Independent Digitized Video System"; and U.S. Pat. No. 5,105,369 to Nelson, entitled "Printing System Exposure Module Alignment Method and Apparatus of Manufacture", each patent being assigned to the same assignee of the present invention and the teachings of each are incorporated herein by reference. Gray scale of the pixels forming the image is achieved by pulse width modulation techniques of the mirrors, such as that described in U.S. Pat. No. 5,278,652, entitled "DMD Architecture and Timing for Use in a Pulse-Width Modulated Display System", assigned to the same assignee of the present invention, and the teachings of which are incorporated herein by reference.
The dimensions of pixel arrays including the DMD array, that is, the number of pixel rows and columns, and the corresponding aspect ratio of the image generated by the pixel array, are designed to conform to one of various national broadcast standards. In the United States, the NTSC is the standard broadcast format to which television displays are designed to meet. In other countries, however, other display format standards are established. For instance, in Europe the PAL broadcast format standard is established. In Japan, the NTSC format standard is established. Thus, the particular national broadcast format standards dictate how pixel images are to be displayed in a particular country. The NTSC format, for instance, sets forth that images will comprise of 480 lines by 640 columns pixels. This corresponds to a 4:3 aspect ratio. The PAL format, however, sets forth that images comprise 576 rows of pixels by 768 columns of pixels, corresponding to a 16:9 aspect ratio.
The DMD is revolutionary in that it is truly a digital display device and an integrated circuit solution. Because the DMD is a digital device, it is well suited for a wide range of hardware and software programmability. It is desired to provide a single hardware programmable pixel array that may be implemented into a display system, and provide an integrated solution over a wide range of video formats. More specifically, it is desirable to provide a hardware programmable pixel array for displaying images compatible with either the NTSC, PAL, and SECAM broadcast formats. This necessitates that the active pixel array be programmable both as to the number of horizontal pixel rows utilized, as well as the number of vertical pixel columns implemented.
In the case of the DMD, it is also desirable to provide a programmable architecture which has a reduced number of package pins to reduce the cost of manufacturing the device. In addition, it is desirable to provide the ability to operate and fully test the device with only a few functional pins. This design would reduce the bandwidth of pixel data and allow the device to be quickly checked out at wafer test with minimal physical damage during probing, which non-functional dies being bypassed or rejected during final optical testing.